[syzbot] [usb?] possible deadlock in tcm_register_callback

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 848acc8ffe1b Merge tag 'fsverity-for-linus' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1113b649580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=642d0d809d2c72babdd2
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/32c9dc084aaa/disk-848acc8f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b7604244b0a9/vmlinux-848acc8f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4cd321f6fe47/bzImage-848acc8f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+642d0d...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.189/7749 is trying to acquire lock:
ffff8880550c4118 (&opts->dep_lock){+.+.}-{4:4}, at: tcm_register_callback+0x1f/0x70 drivers/usb/gadget/function/f_tcm.c:2625

but task is already holding lock:
ffff8880533c7070 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff8880533c7070 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x218/0x4e0 fs/configfs/file.c:229

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&p->frag_sem){++++}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
down_write_killable+0x93/0x250 kernel/locking/rwsem.c:1643
configfs_rmdir+0x3fa/0x950 fs/configfs/dir.c:1534
vfs_rmdir fs/namei.c:5381 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5354
filename_rmdir+0x31a/0x5c0 fs/namei.c:5438
__do_sys_rmdir fs/namei.c:5461 [inline]
__se_sys_rmdir fs/namei.c:5458 [inline]
__x64_sys_rmdir+0x46/0x70 fs/namei.c:5458
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&sb->s_type->i_mutex_key#24){++++}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
inode_lock include/linux/fs.h:1024 [inline]
configfs_depend_item_unlocked+0xf3/0x6a0 fs/configfs/dir.c:1259
usbg_make_tpg+0x261/0x620 drivers/usb/gadget/function/f_tcm.c:1686
target_fabric_make_tpg+0xab/0x8c0 drivers/target/target_core_fabric_configfs.c:939
configfs_mkdir+0x51e/0xb70 fs/configfs/dir.c:1360
vfs_mkdir+0x361/0x850 fs/namei.c:5276
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5309
__do_sys_mkdirat fs/namei.c:5330 [inline]
__se_sys_mkdirat fs/namei.c:5327 [inline]
__x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5327
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&opts->dep_lock){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
tcm_register_callback+0x1f/0x70 drivers/usb/gadget/function/f_tcm.c:2625
usbg_attach drivers/usb/gadget/function/f_tcm.c:2649 [inline]
usbg_enable_tpg+0x95/0x160 drivers/usb/gadget/function/f_tcm.c:1825
target_tpg_enable+0x1fc/0x5d0 drivers/target/target_core_tpg.c:481
target_fabric_tpg_base_enable_store+0x162/0x190 drivers/target/target_core_fabric_configfs.c:840
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
&opts->dep_lock --> &sb->s_type->i_mutex_key#24 --> &p->frag_sem

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(&p->frag_sem);
lock(&sb->s_type->i_mutex_key#24);
lock(&p->frag_sem);
lock(&opts->dep_lock);

*** DEADLOCK ***

4 locks held by syz.2.189/7749:
#0: ffff888021776ef0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1259
#1: ffff88801e736450 (sb_writers#13){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#2: ffff88802bb2dc80 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x76/0x4e0 fs/configfs/file.c:226
#3: ffff8880533c7070 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
#3: ffff8880533c7070 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x218/0x4e0 fs/configfs/file.c:229

stack backtrace:
CPU: 0 UID: 0 PID: 7749 Comm: syz.2.189 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
tcm_register_callback+0x1f/0x70 drivers/usb/gadget/function/f_tcm.c:2625
usbg_attach drivers/usb/gadget/function/f_tcm.c:2649 [inline]
usbg_enable_tpg+0x95/0x160 drivers/usb/gadget/function/f_tcm.c:1825
target_tpg_enable+0x1fc/0x5d0 drivers/target/target_core_tpg.c:481
target_fabric_tpg_base_enable_store+0x162/0x190 drivers/target/target_core_fabric_configfs.c:840
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f72db79e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f72dc5e0028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f72dba25fa0 RCX: 00007f72db79e019
RDX: 0000000000000001 RSI: 00002000000009c0 RDI: 0000000000000007
RBP: 00007f72db83500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f72dba26038 R14: 00007f72dba25fa0 R15: 00007ffdfd368f88
</TASK>
UDC core: g1: couldn't find an available UDC or it's busy


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